We are identifying families in which multiple first-degree members have a diagnosis of obsessive-compulsive disorder (OCD). These families are being identified from any source, including referrals from Johns Hopkins clinicians and private therapists in the community. The subjects are being examined by psychiatrists and clinical psychologists. The aim is to clinically evaluate all the family members and to obtain a blood sample from each. Cell lines for future DNA extraction are being developed. To date, we have clinically examined 31 subjects in 15 families identified in this manner, and obtained blood samples from them. Once an adequate number of subjects has been interviewed and blood samples collected, we will be poised to proceed to genetic studies of these families, including both linkage and association strategies. The ultimate goal is to identify gene(s) involved in the development of the disorder. This will clarify the pathophysiology of OCD and lead to more rational treatments.